The protection of weatherable substrates has long been a desired goal. The ideal weatherable coating composition will provide desirable protection against the elements, will not discolor or otherwise mar the appearance of the surface to be protected, and will sufficiently fill holes and bridge gaps in irregularly surfaced substrates. Moreover, such a sealant composition must be readily applied and cured.
Among the polymeric materials which have been employed in the past for the protection of weatherable substrates are certain moisture-curable high molecular weight silane-grafted rubbery polymers. Thus, for example, Kresge et al (in U.S. Pat. No. 3,503,943) show moisture-curable silane-grafted copolymers having an ethylene/propylene/nonconjugated diene backbone, which polymers may be employed to form a waterproof protective layer. It is noteworthy that all the graft copolymers actually made by Kresge et al have an inherent viscosity of more than 2.0 dl/g in tetralin and thus possess molecular weights of more than about 90,000.
Somewhat similarly, Gardner et al (in U.S. Pat. No. 3,644,315) show moisture-curable silane-grafted conjugated diolefin polymers having at least 0.5 mole percent unsaturation in their backbones. It is to be noted that the lowest molecular weight of any backbone polymer shown in the examples of Gardner et al is more than 40,000. See also U.S. Pat. No. 3,646,155 to Scott, which shows the use of silane grafting to crosslink high molecular weight polyethylene resins.
Although Kresge et al and Gardner et al, discussed above, do state that lower molecular weight backbone polymers may be employed, these patents do not exemplify this statement. In this regard, the conclusions of the survey article presented by G. Wouters and F. Woods entitled "Moisture-Curable Silane Grafted Ethylene Propylene Elastomers" and presented at the International Rubber Conference 1981, Harrogate, U.K.--i.e., almost 10 years after the issuance of the Kresge et al and Gardner et al patents--is extremely noteworthy. Specifically, in Table 5 of their presentation, Wouters et al conclude that "EPM's or EPDM's with low molecular weight" are "structures with low moisture-curing potential."
A second class of polymeric materials which have been employed to produce moisture-curable sealants are silane-grafted halogenated copolymers. Thus, Baldwin et al (in U.S. Pat. No. 3,366,612) show certain halogenated polymeric compositions which have been reacted with silanes to form materials useful as waterproof, weather-resistant liners. Somewhat similarly, Bond, Jr. et al (in U.S. Pat. No. 4,028,483) show interpolymers of ethylene, propylene and an ethylenically unsaturated silane substituted with a "highly hydrolyzable group" (in all examples a halogen or halogenated group).
A third class of moisture-curable polymers which have been disclosed as being useful for the protection of certain substrates (e.g., metal, glass or plastic fibers) from adverse environmental conditions are low molecular weight silane-modified waxes. Thus, Inakaki et al (in Japanese Patent Disclosure No. 1979-145785) show low molecular weight silane-grafted waxes which are suitable for fabrication by casting above their melt temperature of 80.degree.-160.degree. C.
In addition, Joffrion (in U.S. Pat. No. 4,340,689) and Swarbrick et al (in U.S. Pat. No. 4,117,195) show methods of grafting silanes onto ethylene/alphaolefin copolymers.
While all three types of polymers discussed above will provide some degree of protection to certain weatherable substrates, there are drawbacks associated with the uses of each. Thus, high molecular weight polymers will not desirably penetrate into porous substrates and, upon evaporation of the solvent required for their application, are prone to contraction thereby leaving portions of the substrates unprotected.
Halogenated polymers (which, if of high molecular weight will additionally possess the drawbacks disclosed above) liberate mineral acids, frequently potent acids such as hydrochloric acid, upon curing. Such acids may discolor the protective coating or even attack the substrate itself.
Waxes possess the disadvantage that they must be heated above their melt temperature of 80.degree.-120.degree. C. before being employed. Not only do such high temperatures cause difficulty in application, but they may harm the substrate to be protected as well.
Thus, it would be highly desirable to possess a coating composition which could be easily applied, would exhibit good penetration of porous substrates and which would not impair the appearance of the substrate to be protected.
Accordingly, it is an object of this invention to provide a coating composition which is easily applied and which will not impair the appearance of the substrate to be protected.
It is a further object of this invention to provide a coating composition which exhibits desirable penetration into porous substrates and which does not require the use of large amounts of solvent.
It is another object of this invention to provide a novel silane-substituted polymer which is useful in coating compositions.
It is yet another object of this invention to provide a method of protecting a weatherable substrate.
It is another object of this invention to provide a composite comprised of a weatherable substrate and a protective polymeric layer.
These objects, and other additional objects, will become more fully apparent from the following description and accompanying Examples.